The present invention relates to a process for the production of highly dispersed pigment concentrates which can be used to replace the traditional so called Flush concentrates.
In contrast to the flushing process, the subject of the current invention is a process based on dry, granular feed-stock and not on a water-containing pigmented feed-stock, (e.g. presscake) commonly used. The aforementioned concentrates are useful in the colouration of printing inks especially lithographic printing inks.
Methods are known for formulating pigment compositions, which include a carrier to produce a composition which is in a non-powder form. The carriers used in such systems are selected to optimise the incorporation of the pigmented composition produced into the final applicational medium. Conventionally such compositions would be produced from water-containing pigmented feedstocks of 3-40% pigment content, the underlying principle being that an organic pigment has a greater affinity for an oil phase than an aqueous phase and so transfers or flushes from the aqueous environment to the carrier. Pigments have been flushed into a variety of vehicles from the 1860""s but it was not until 1914 that pigment flushing as it is commonly known today was invented by Robert Hochstedder. The flush process features and the equipment used have been the subject of much investigation which has resulted in many disclosures of various improvements in the basic concept. However, to date all processes have been based on the use of water-containing pigmented feedstocks, e.g. aqueous press-cakes for reasons described in many publications e.g. Pigment Handbook, Vol 111, (1973) p447-455, Editor T C Patton, Printing Ink Manual, 4th Edition (1989), p602-604, Edited by R H Leach, Printing Ink Technology (1958) p498-502, EA Apps, Industrial Printing Inks (1962), p144-145, L M Larsen J K Randolph European Polymers Paint Colour Journal, Apr. 27, 1994. The basic principle behind the use of, e.g. press-cakes in the flush process to produce high quality dispersions as well as the aforementioned organophilic nature of the pigment is that organic pigments undergo irreversible aggregation/agglomeration during the drying process of manufacture and thus can not effectively flush and so are poorly dispersed, resulting in pigmented concentrates which give undesirable applicational results as described in, e.g. JP Sho 61-23916 (1986), U.S. Pat. No. 4,601,759 (1986), EP 273,236 (1982). As well as processes using press-cakes, more recently, processes have been disclosed whereby the flushing process has been carried out xe2x80x98in-vatxe2x80x99 directly after the completion of synthesis of the pigment and prior to filtration as described in, e.g. WO8912075 (1989), U.S. Pat. No. 4,765,841 (1988), U.S. Pat. No. 4255375 (1981) and EP319,628,B (1987). These processes produce bead-like products which have then been used like the more traditional flushed concentrates as described in some of the above mentioned publications. In the flush procedure these aforementioned publications describe the equipment traditionally used in the flush process as being high energy mixers or kneaders, e.g. Sigma-blade kneaders. During the process the aqueous phase is removed by decantation and further, e.g. press-cake and carrier added whereupon the process repeated until-the desired flush concentrate is achieved. While the use of such flushing techniques avoids certain problems e.g. hydrophilic aggregation on drying, grinding treatment and dusting associated with conventional pigment powder production, flushing processes are not without disadvantages e.g.
1. Standardisation of final coloured concentrate due to the use of non-standardised press-cake.
2. The pigment performance when held in presscake form varies with time and conditions of storage.
3. Energy costs associated with effluent treatment of the discarded aqueous phase which also may contain oils.
4. Energy costs not only for the kneading process but also for the drying of the flush to remove all water.
5. The total cycle times are relatively long to produce the final coloured coating agent e.g. printing ink typically 6-18 hours.
6. The use of agents to promote the flushing process e.g. surfactants.
7. Press-cakes of organic pigments are liable to microbiological attack and though it is possible to add biocides/fungicides, the presence of these are undesirable in lithographic inks.
It is thus surprising that we have found a process which overcomes all these disadvantages and introduces other advantages.
Accordingly the present invention provides a process for the manufacture of a pigment concentrate which comprises dispersing dry organic pigment granules in an organic vehicle.
The key to this invention is the use of dry granular pigment instead of water-containing pigmented feed-stocks (thus avoiding the flush procedure) which do not result in the disadvantages of dry pigment as described herein above, viz very slow rates of dispersion, poor final levels of dispersion and consequently poor quality final inks. Indeed using the same equipment as for flushing, dry granular products as described herein are very rapidly and highly dispersed producing final inks which are at least as good as those derived from a conventional feed-stock. Thus the herein defined dry granular products result in highly dispersed concentrates via processes currently used with water containing pigment compositions, e.g. pigmented press-cakes but with significant advantages over the conventional flush process viz.
1. Like press-cake the granular products are non-dusting but are more easily handled and meterable, making dosing easier and more accurate.
2. Since the granular products are dried during the manufacture then no aqueous waste treatment is required.
3. Processing times are significantly reduced due to the rapid rate of dispersion of the granules.
4. Energy consumption is reduced since the drying step of the flush process is removed.
5. Batch sizes are increased by use of the dry pigmented granules.
6. The granules are standardised prior to use as part of their manufacturing process.
7. Since press-cakes of organic pigments are liable to biological attack resulting in deterioration of applicational performance in terms of colouristics then this is overcome by the use of the dry standardised granules.
8. No flush enhancing additives are required.
9. Conventional equipment is used as for press-cakes.
In particular as well as significantly reduced processing costs the machine time, i.e. cycle time is between 14 hrs but normally between 1-2 hrs depending on the pigment used compared to the 5-16 hours cycle time using the traditional flush process.
The pigment granules used in this process are based on conventional organic pigments including azo, azomethene, copper phthalocyanines, anthraquinones, nitro, perinone, quinacridone, azo or azomethene metal salts or complexes and dipyrolopyrole. Mixtures of pigments may also be used. The pigment, used in this process may or may not be surface treated e.g. using treatments normally applied to pigments for use in oil ink systems. The treatments may comprise additives which are natural or synthetic resins which may be in non-salt form or in salt form.
Examples of such resins include rosin, the principal component of which is abeitic acid; also modified rosin such as hydrogenated, dehydrogenated or disproportionated rosin, dimersed or polymerised rosin, partially esterified rosin, non-esterified or partially esterfied maleic or phenolic modified rosin. Illustrative rosins include such commercially available materials as Staybelite resin (hydrogenated rosin), Recoldis A resin (disproportionated rosin) and Dymerex resin (dimersed rosin). The additive may also be an amine, e.g. rosin amine D (dehydroabietyl amine).
As part of this water-soluble salt additive it is also optional that a non-polar component be present as described in our patent U.S. Pat. No. 5,366,546.
Non-polar components, which may be added to the polar pigment additive may be, but are not limited to, rosin-modified phenolic resins, rosin-modified maleic resins, hydrocarbon resins, alkyd resins, phenolic resins, fatty alcohols, drying, semi-drying or non-drying oils, polyolefins, waxes, litho varnishes, or gloss varnishes.
The dry granular pigment used in the present invention is a low dusting meterable material with a mean size of 0.1 to 50 mm but more preferably 0.1-20 mm. Also the term dry is understood to refer to 05.0% moisture but more normally 02.0% residual moisture. The granules herein disclosed are conveniently prepared by a range of known methods and include as examples wet granulation using a extruder granulator followed by conventional drying of the granular extrudate, as described in Japanese laid open patent 52568/1983 spray drying as described in U.S. Pat. No. 3,843,380, in-vat granulation as described in U.S. Pat. No. 4,255,375 or fluid-bed granulation as described for example in GB2036057.
The carrier vehicles into which to pigment granules are dispersed are usually hydrophobic, are dependant upon the final application area and include but are not restricted to the following viz, printing ink varnishes including those used in heatset, cold set and sheetfed inks, lithographic inks, news inks, varnish tin printing inks, thermoplastic resins and waxes, such as high density polyethylene, low density polyethylene, polyethylene waxes and polypropylene plastics.
The process of manufacture of the dispersed pigment concentrates of the invention may use equipment currently used by manufacturers of coloured concentrates based on water containing pigmented feed-stocks, i.e. flush, and includes for example kneaders, extruders, high energy mixers but preferably kneaders of the Z-blade type.
The dispersed pigment concentrates so produced by this process have a pigment concentration ranging from 20-75% but preferably from 30-60%. The process of manufacture for example using conventional kneaders e.g. of the Z-blade type is most conveniently but not exclusively carried out by adding the appropriate amount of carrier, for example a printing ink varnish, mixing said varnish in the mixer, then metering in the appropriate quantity of granules over a period of 1-20 mins but more normally 2-5 minutes to produce a pulp of 40-80% pigment concentration but more ideally 50-65%. The granules rapidly wet out and are dispersed after 5-45 minutes but more often over 5-30 minutes. The resulting fully dispersed viscous pulp is then diluted by careful addition of carrier vehicle e.g. ink varnish and if required any other desired additives to the required pigmentation level of the final concentrate. The concentrate is then discharged for use in the appropriate application at the required pigmentation level.
The final inks produced by to above process are at least equivalent in quality to those produced via the traditional flush process.
The invention is illustrated by to following Examples.